Lemma 2.10 ([1]})  If \([L,B]=0\)  then there exists a polynomial in two variables \(f(\lambda ,\mu )\in {\bf C}[\lambda ,\mu ]\)  such that \(f(L,B)\equiv 0\) , if we assign “weight” \(na+mb\)  to a monomial \(\lambda ^a\mu ^b\)  where \(n=\operatorname{ord}L\) , \(m=\operatorname{ord}B\) , \(\gcd (n,m)=1\) , then the terms of highest weight in \(f\)  are \(\alpha \lambda ^m+\beta \mu ^n\)  for
some constants \(\alpha \) , \(\beta \) .

